Abstract: GCTS Hollow Cylinder apparatus is the best tool to study the soil behavior under the principal stress rotation. In the whole process of torsional shear test, saturation of specimen is prerequisite and the success of the samples saturated also is the key. Taking GCTS hollow cylinder apparatus as a testing platform, the back pressure method is used to saturate hydraulic fill fully. The apparatus provides 3 ways to increase confining pressure and back pressure, i. e. manual stepping, automatic stepping and continuous ramping. Through some experiments, each compression of the corresponding parameters reasonable is explored. 15kpa differential pressure be adequate for hydraulic fill. The standards of pore pressure stability.. If the changes of porepressure in one minute is less than the 5%of difference between the cell pressure and the back pressure, the pore pressure is considered stable.